[DOCS] Paged Content display out of date with Starter site re available contexts

[kayakr]

• If applicable, link to the documentation page relevant to your issue below.
  https://islandora.github.io/documentation/user-documentation/iiif/#using-iiif-in-islandora

• Describe your documentation request.
  "Using IIIF in the Islandora Starter Site" describes using a context "Paged Content - Openseadragon Context" to display paged content. However, in current Starter Site https://sandbox.islandora.ca/admin/structure/context no such context exists, instead the contexts are "Mirador Block - Multipaged items", and "Openseadragon Block - Multipaged items".

[ysuarez]

I can create a PR for this and have you verify it.